In computer architecture , 16-BIT integers , memory addresses , or
other data units are those that are 16 bits (2 octets) wide. Also,
16-bit CPU and ALU architectures are those that are based on registers
, address buses , or data buses of that size.
16-bit microcomputers
are computers in which
16-bit microprocessors were the norm.

A
16-bit register can store 216 different values. The signed range of
integer values that can be stored in 16 bits is −32,768 (−1 ×
215) through 32,767 (215 − 1); the unsigned range is 0 through
65,535 (216 − 1). Since 216 is 65,536, a processor with 16-bit
memory addresses can directly access 64 KiB of byte-addressable
memory. If a system uses segmentation with
16-bit segment offsets,
more can be accessed.

A
16-bit integer can store 216 (or 65,536) distinct values. In an
unsigned representation, these values are the integers between 0 and
65,535; using two\'s complement , possible values range from −32,768
to 32,767. Hence, a processor with
16-bit memory addresses can
directly access 64 KB of byte-addressable memory.

16-bit processors have been almost entirely supplanted in the
personal computer industry, and are used less than
32-bit (or 8-bit)
CPUs in embedded applications.

16/32-BIT MOTOROLA 68000 AND INTEL 386SX

The
Motorola 68000 is sometimes called _16-bit_ because its internal
and external data buses were 16 bits wide, however it could be
considered a
32-bit processor in that the general purpose registers
were 32 bits wide and most arithmetic instructions supported 32-bit
arithmetic. The 68000 was a microcoded processor with three internal
16-bit ALU units. Only 24-bits of the program counter (PC) were
available on original DIP packages, with up to 16 megabytes of
addressable RAM . 68000 software is
32-bit in nature and
forward-compatible with other
32-bit processors in the same family.
The 68008 was a version of the 68000 with
8-bit external data path and
1 megabyte addressing for the 48-pin DIP version and 4 megabyte for
the 52-pin PLCC version. Several
Apple Inc.Macintosh models; e.g., LC
series, used
32-bit 68020 and 68030 processors on a
16-bit data bus to
save cost.

Similar analysis applies to Intel's
80286 CPU replacement called the
386SX which is a
32-bit processor with
32-bit ALU and internal 32-bit
data paths with a
16-bit external bus and 2
4-bit addressing of the
processor it replaced.

The 68000 processor of the
Sega Genesis was a highly advertised
feature of the video game system. Due to the saturation of this
advertising, the 1988–95 era (fourth generation ) of video game
consoles is often called _the
16-bit era_.

Just as there are multiple data models for 6
4-bit architectures , the
16-bitIntel architecture allows for different memory models—ways to
access a particular memory location. The reason for using a specific
memory model is the size of the assembler instructions or required
storage for pointers. Compilers of the
16-bit era generally had the
following type-width characteristic:

Tiny Code and data will be in the same segment (especially, the
registers CS, DS, ES, SS will point to the same segment); _near_
(16-bit) pointers are always used. Code, data and stack together
cannot exceed 64 KB. Small Code and data will be in different
segments, and near pointers are always used. There will be 64 KB of
space for code and 64 KB for data/stack. Medium Code pointers will use
_far_ pointers (16:16 bit), enabling access to 1 MB. Data pointers
remain to be of the near type. Compact Data pointers will use far and
code will use near pointers. Large/huge Code and data pointers will be
far.

16-BIT APPLICATION

In the context of
IBM PC compatible and
Wintel platforms, a 16-bit
application is any software written for
MS-DOS ,
OS/2 1.x or early
versions of
Microsoft Windows which originally ran on the
16-bit Intel
8088 and
Intel 80286 microprocessors . Such applications used a 20-bit
or 2
4-bit segment or selector-offset address representation to extend
the range of addressable memory locations beyond what was possible
using only
16-bit addresses. Programs containing more than 216 bytes
(64 kilobytes ) of instructions and data therefore required special
instructions to switch between their 64-kilobyte segments , increasing
the complexity of programming
16-bit applications.

* Microprocessor:
16-bit designs
* Influence of the
IBM PC on the personal computer market: Before
the
IBM PC\'s introduction
* 74181 (key component of some early
16-bit and other CPUs)
*
Audio bit depth – as
16-bit is the most common bit depth used,
e.g. on
CD audio .

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